Process for production of acrylic acid

ABSTRACT

Provided are integrated processes for the conversion of beta propiolactone to acrylic acid. Systems for the production of acrylic acid are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/116,325, filed Feb. 13, 2015, which is incorporated herein byreference in its entirety.

FIELD

The present disclosure relates generally to the production of acrylicacid, and more specifically to the production of acrylic acid from betapropiolactone.

BACKGROUND

Superabsorbent polymers (SAPs) are used in a variety of industrial andconsumer applications, ranging from disposable hygiene products to cablewater blocking. SAPs are mostly commonly manufactured by polymerizationof acrylic acid. Acrylic acid production is a large industry that usesvariety of methods having a range of cost efficiencies and yieldingacrylic acid of varying purity. Given the size of the acrylic acidmarket and the importance of downstream applications of acrylic acid,there is a need for methods for producing acrylic acid with increasedefficiency.

Methods have been described where beta propiolactone (BPL) is convertedto acrylic acid (AA) by heating in the presence of water or alcohols,which act as catalysts to open the BPL to hydracrylic acid (3-hydroxypropionic acid) or hydracrylic acid esters, respectively. However, thesemethods are ill-suited to the production of glacial acrylic acid (GAA)because the water or alcohol used to catalyze the reaction cancontaminate the acrylic acid stream. Thus, alternative methods toproduce acrylic acid are desired.

BRIEF SUMMARY

In some aspects, provided is a method for producing acrylic acid,comprising:

-   -   (a) providing a feedstock stream comprising beta propiolactone;    -   (b) directing the feedstock stream to a reaction zone where it        is contacted with a suitable polymerization catalyst and where        at least a portion of the beta propiolactone is converted to        poly(propiolactone);    -   (c) maintaining the reaction zone at a temperature at or above        the pyrolysis temperature of poly(propiolactone) such that the        thermal decomposition of poly(propiolactone) produces acrylic        acid; and    -   (d) withdrawing an acrylic acid product stream from the reaction        zone;    -   wherein steps (b) and (c) occur in the same reaction zone.

In other aspects, provided is a method for producing acrylic acid,comprising:

-   -   (a) providing a feedstock stream comprising beta propiolactone;    -   (b) directing the feedstock stream to a first reaction zone,        wherein the feedstock stream is contacted with a polymerization        catalyst and wherein at least a portion of the beta        propiolactone is converted to a poly(propiolactone) product        stream, wherein the first reaction zone is maintained at a        temperature suitable for the formation of poly(propiolactone);    -   (c) directing the poly(propiolactone) product stream to a second        reaction zone, wherein the second reaction zone is maintained at        a temperature at or above the pyrolysis temperature of        poly(propiolactone) such that the thermal decomposition of        poly(propiolactone) produces acrylic acid; and    -   (d) withdrawing an acrylic acid product stream from the second        reaction zone.

In other aspects, provided is a system for converting beta propiolactoneto acrylic acid, comprising:

-   -   (a) beta propiolactone; and    -   (b) a cationic solid catalyst comprising a carboxylate salt;    -   wherein at or above the pyrolysis temperature of        poly(propiolactone), beta propiolactone begins polymerizing to        poly(propiolactone) in the presence of the cationic solid        catalyst, which poly(propiolactone) concurrently thermally        decomposes to acrylic acid; and    -   wherein acrylic acid formed in situ maintains the reaction        polymerizing beta propiolactone to poly(propiolactone).

In yet other aspects, provided is a system for converting betapropiolactone to acrylic acid, comprising:

-   -   (a) a reaction zone comprising beta propiolactone (BPL) and a        cationic solid catalyst comprising a carboxylate salt;    -   wherein at or above the pyrolysis temperature of        poly(propiolactone) (PPL). BPL begins polymerizing to PPL, which        PPL concurrently thermally decomposes to acrylic acid; and    -   (b) a return loop for providing acrylic acid to the reaction        zone.

Definitions

Definitions of specific functional groups and chemical terms aredescribed in more detail below. The chemical elements are identified inaccordance with the Periodic Table of the Elements, CAS version,Handbook of Chemistry and Physics, 75^(th) Ed., inside cover, andspecific functional groups are generally defined as described therein.Additionally, general principles of organic chemistry, as well asspecific functional moieties and reactivity, are described in OrganicChemistry, Thomas Sorrell, University Science Books, Sausalito, 1999;Smith and March March's Advanced Organic Chemistry, 5^(th) Edition, JohnWiley & Sons, Inc., New York, 2001; Larock, Comprehensive OrganicTransformations, VCH Publishers, Inc., New York, 1989; Carruthers, SomeModern Methods of Organic Synthesis, 3^(rd) Edition, CambridgeUniversity Press, Cambridge, 1987.

The terms “halo” and “halogen” as used herein refer to an atom selectedfrom fluorine (fluoro, —F), chlorine (chloro, —Cl), bromine (bromo,—Br), and iodine (iodo, —I).

The term “aliphatic” or “aliphatic group”, as used herein, denotes ahydrocarbon moiety that may be straight-chain (i.e., unbranched),branched, or cyclic (including fused, bridging, and spiro-fusedpolycyclic) and may be completely saturated or may contain one or moreunits of unsaturation, but which is not aromatic. In some variations,the aliphatic group is unbranched or branched. In other variations, thealiphatic group is cyclic. Unless otherwise specified, in somevariation, aliphatic groups contain 1-30 carbon atoms. In someembodiments, aliphatic groups contain 1-12 carbon atoms. In someembodiments, aliphatic groups contain 1-8 carbon atoms. In someembodiments, aliphatic groups contain 1-6 carbon atoms. In someembodiments, aliphatic groups contain 1-5 carbon atoms, in someembodiments, aliphatic groups contain 1-4 carbon atoms, in yet otherembodiments aliphatic groups contain 1-3 carbon atoms, and in yet otherembodiments aliphatic groups contain 1-2 carbon atoms. Suitablealiphatic groups include, for example, linear or branched, alkyl,alkenyl, and alkynyl groups, and hybrids thereof such as(cycloalkyl)alkyl, (cycloalkenyl)alkyl or (cycloalkyl)alkenyl.

The term “heteroaliphatic,” as used herein, refers to aliphatic groupswherein one or more carbon atoms are independently replaced by one ormore atoms selected from the group consisting of oxygen, sulfur,nitrogen, phosphorus, or boron. In some embodiments, one or two carbonatoms are independently replaced by one or more of oxygen, sulfur,nitrogen, or phosphorus. Heteroaliphatic groups may be substituted orunsubstituted, branched or unbranched, cyclic or acyclic, and include“heterocycle,” “hetercyclyl,” “heterocycloaliphatic,” or “heterocyclic”groups. In some variations, the heteroaliphatic group is branched orunbranched. In other variations, the heteroaliphatic group is cyclic. Inyet other variations, the heteroaliphatic group is acyclic.

The term “acrylate” or “acrylates” as used herein refer to any acylgroup having a vinyl group adjacent to the acyl carbonyl. The termsencompass mono-, di- and tri-substituted vinyl groups. Acrylates mayinclude, for example, acrylate, methacrylate, ethacrylate, cinnamate(3-phenylacrylate), crotonate, tiglate, and senecioate.

The terms “crude acrylic acid” and “glacial acrylic acid”, as usedherein, describe acrylic acid of relatively low and high purity,respectively. Crude acrylic acid (also called technical grade acrylicacid) has a typical minimum overall purity level of 94% and can be usedto make acrylic esters for paint, adhesive, textile, paper, leather,fiber, and plastic additive applications. Glacial acrylic acid has atypical overall purity level ranging from 98% to 99.99% and can be usedto make polyacrylic acid for superabsorbent polymers (SAPs) indisposable diapers, training pants, adult incontinence undergarments andsanitary napkins. Polyacrylic acid is also used in compositions forpaper and water treatment, and in detergent co-builder applications. Insome variations, acrylic acid has a purity of at least 98%, at least98.5%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, atleast 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least99.8%, or at least 99.9%; or between 99% and 99.95%, between 99.5% and99.95%, between 99.6% and 99.95%, between 99.7% and 99.95%, or between99.8% and 99.95%.

Impurities in glacial acrylic acid are reduced to an extent possible tofacilitate a high-degree of polymerization to acrylic acid polymers(PAA) and avoid adverse effects from side products in end applications.For example, aldehyde impurities in acrylic acid hinder polymerizationand may discolor the polymerized acrylic acid. Maleic anhydrideimpurities form undesirable copolymers which may be detrimental topolymer properties. Carboxylic acids, e.g., saturated carboxylic acidsthat do not participate in the polymerization, can affect the final odorof PAA or SAP-containing products and/or detract from their use. Forexample, foul odors may emanate from SAP that contains acetic acid orpropionic acid and skin irritation may result from SAP that containsformic acid. The reduction or removal of impurities from petroleum-basedacrylic acid is costly, whether to produce petroleum-based crude acrylicacid or petroleum-based glacial acrylic acid. Such costly multistagedistillations and/or extraction and/or crystallizations steps aregenerally employed (e.g., as described in U.S. Pat. Nos. 5,705,688 and6,541,665).

The term “polymer”, as used herein, refers to a molecule comprisingmultiple repeating units. In some variations, the polymer is a moleculeof high relative molecular mass, the structure of which comprises themultiple repetition of units derived, actually or conceptually, frommolecules of low relative molecular mass. In some embodiments, a polymeris comprised of only one monomer species (e.g., polyethylene oxide). Insome embodiments, the polymer is a copolymer, terpolymer, heteropolymer,block copolymer, or tapered heteropolymer of one or more epoxides. Inone variation, the polymer may be a copolymer, terpolymer,heteropolymer, block copolymer, or tapered heteropolymer of two or moremonomers.

The term “unsaturated”, as used herein, means that a moiety has one ormore double or triple bonds.

The terms “cycloaliphatic”, “carbocycle”, or “carbocyclic”, used aloneor as part of a larger moiety, refer to a saturated or partiallyunsaturated cyclic aliphatic monocyclic, bicyclic, or polycyclic ringsystems, as described herein, having from 3 to 12 members, wherein thealiphatic ring system is optionally substituted as defined above anddescribed herein. Cycloaliphatic groups include, for example,cyclopropyl, cyclobutyl, cyclopentyl, cyclopentenyl, cyclohexyl,cyclohexenyl, cycloheptyl, cycloheptenyl, cyclooctyl, cyclooctenyl, andcyclooctadienyl. In some embodiments, the cycloalkyl has 3-6 carbons.The terms “cycloaliphatic”. “carbocycle” or “carbocyclic” also includealiphatic rings that are fused to one or more aromatic or nonaromaticrings, such as decahydronaphthyl or tetrahydronaphthyl, where theradical or point of attachment is on the aliphatic ring. In someembodiments, a carbocyclic groups is bicyclic. In some embodiments, acarbocyclic group is tricyclic. In some embodiments, a carbocyclic groupis polycyclic.

The term “alkyl,” as used herein, refers to a saturated hydrocarbonradical. In some variations, the alkyl group is a saturated, straight-or branched-chain hydrocarbon radicals derived from an aliphatic moietycontaining between one and six carbon atoms by removal of a singlehydrogen atom. Unless otherwise specified, in some variations, alkylgroups contain 1-12 carbon atoms. In some embodiments, alkyl groupscontain 1-8 carbon atoms. In some embodiments, alkyl groups contain 1-6carbon atoms. In some embodiments, alkyl groups contain 1-5 carbonatoms, in some embodiments, alkyl groups contain 1-4 carbon atoms, inyet other embodiments alkyl groups contain 1-3 carbon atoms, and in yetother embodiments alkyl groups contain 1-2 carbon atoms. Alkyl radicalsmay include, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl,iso-butyl, sec-butyl, sec-pentyl, iso-pentyl, tert-butyl, n-pentyl,neopentyl, n-hexyl, sec-hexyl, n-heptyl, n-octyl, n-decyl, n-undecyl,and dodecyl.

The term “alkenyl,” as used herein, denotes a monovalent group having atleast one carbon-carbon double bond. In some variations, the alkenylgroup is a monovalent group derived from a straight- or branched-chainaliphatic moiety having at least one carbon-carbon double bond by theremoval of a single hydrogen atom. Unless otherwise specified, in somevariations, alkenyl groups contain 2-12 carbon atoms. In someembodiments, alkenyl groups contain 2-8 carbon atoms. In someembodiments, alkenyl groups contain 2-6 carbon atoms. In someembodiments, alkenyl groups contain 2-5 carbon atoms, in someembodiments, alkenyl groups contain 2-4 carbon atoms, in yet otherembodiments alkenyl groups contain 2-3 carbon atoms, and in yet otherembodiments alkenyl groups contain 2 carbon atoms. Alkenyl groupsinclude, for example, ethenyl, propenyl, butenyl, and1-methyl-2-buten-1-yl.

The term “alkynyl,” as used herein, refers to a monovalent group havingat least one carbon-carbon triple bond. In some variations, the alkynylgroup is a monovalent group derived from a straight- or branched-chainaliphatic moiety having at least one carbon-carbon triple bond by theremoval of a single hydrogen atom. Unless otherwise specified, in somevariations, alkynyl groups contain 2-12 carbon atoms. In someembodiments, alkynyl groups contain 2-8 carbon atoms. In someembodiments, alkynyl groups contain 2-6 carbon atoms. In someembodiments, alkynyl groups contain 2-5 carbon atoms, in someembodiments, alkynyl groups contain 2-4 carbon atoms, in yet otherembodiments alkynyl groups contain 2-3 carbon atoms, and in yet otherembodiments alkynyl groups contain 2 carbon atoms. Representativealkynyl groups include, for example, ethynyl, 2-propynyl (propargyl),and 1-propynyl.

The term “carbocycle” and “carbocyclic ring” as used herein, refers tomonocyclic and polycyclic moieties wherein the rings contain only carbonatoms. Unless otherwise specified, carbocycles may be saturated,partially unsaturated or aromatic, and contain 3 to 20 carbon atoms.Representative carbocyles include, for example, cyclopropane,cyclobutane, cyclopentane, cyclohexane, bicyclo[2,2,1]heptane,norbomene, phenyl, cyclohexene, naphthalene, and spiro[4.5]decane.

The term “aryl” used alone or as part of a larger moiety as in“aralkyl”, “aralkoxy”, or “aryloxyalkyl”, refers to monocyclic andpolycyclic ring systems having a total of five to 20 ring members,wherein at least one ring in the system is aromatic and wherein eachring in the system contains three to twelve ring members. The term“aryl” may be used interchangeably with the term “aryl ring”. In someembodiments, “aryl” refers to an aromatic ring system which includes,for example, phenyl, naphthyl, and anthracyl, which may bear one or moresubstituents. Also included within the scope of the term “aryl”, as itis used herein, is a group in which an aromatic ring is fused to one ormore additional rings, such as benzofuranyl, indanyl, phthalimidyl,naphthimidyl, phenanthridinyl, and tetrahydronaphthyl.

The terms “heteroaryl” and “heteroar-”, used alone or as part of alarger moiety, e.g., “heteroaralkyl”, or “heteroaralkoxy”, refer togroups having 5 to 14 ring atoms, preferably 5, 6, 9 or 10 ring atoms;having 6, 10, or 14 pi (π) electrons shared in a cyclic array; andhaving, in addition to carbon atoms, from one to five heteroatoms. Theterm “heteroatom” refers to nitrogen, oxygen, or sulfur, and includesany oxidized form of nitrogen or sulfur, and any quaternized form of abasic nitrogen. Heteroaryl groups include, for example, thienyl,furanyl, pyrrolyl, imidazolyl, pyrazolyl, triazolyl, tetrazolyl,oxazolyl, isoxazolyl, oxadiazolyl, thiazolyl, isothiazolyl,thiadiazolyl, pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, indolizinyl,purinyl, naphthyridinyl, benzofuranyl and pteridinyl. The terms“heteroaryl” and “heteroar-”, as used herein, also include groups inwhich a heteroaromatic ring is fused to one or more aryl,cycloaliphatic, or heterocyclyl rings, where the radical or point ofattachment is on the heteroaromatic ring. Examples include indolyl,isoindolyl, benzothienyl, benzofuranyl, dibenzofuranyl, indazolyl,benzimidazolyl, benzthiazolyl, quinolyl, isoquinolyl, cinnolinyl,phthalazinyl, quinazolinyl, quinoxalinyl, 4H-quinolizinyl, carbazolyl,acridinyl, phenazinyl, phenothiazinyl, phenoxazinyl,tetrahydroquinolinyl, tetrahydroisoquinolinyl, andpyrido[2,3-b]-1,4-oxazin-3(4H)-one. A heteroaryl group may be mono- orbicyclic. The term “heteroaryl” may be used interchangeably with theterms “heteroaryl ring”, “heteroaryl group”, or “heteroaromatic”, any ofwhich terms include rings that are optionally substituted. The term“heteroaralkyl” refers to an alkyl group substituted by a heteroaryl,wherein the alkyl and heteroaryl portions independently are optionallysubstituted.

As used herein, the terms “heterocycle”, “heterocyclyl”, “heterocyclicradical”, and “heterocyclic ring” are used interchangeably and may besaturated or partially unsaturated, and have, in addition to carbonatoms, one or more, preferably one to four, heteroatoms, as definedabove. In some variations, the heterocyclic group is a stable 5- to7-membered monocyclic or 7- to 14-membered bicyclic heterocyclic moietythat is either saturated or partially unsaturated, and having, inaddition to carbon atoms, one or more, preferably one to four,heteroatoms, as defined above. When used in reference to a ring atom ofa heterocycle, the term “nitrogen” includes a substituted nitrogen. Asan example, in a saturated or partially unsaturated ring having 0-3heteroatoms selected from oxygen, sulfur or nitrogen, the nitrogen maybe N (as in 3,4-dihydro-2H-pyrrolyl), NH (as in pyrrolidinyl), or NR (asin N-substituted pyrrolidinyl).

A heterocyclic ring can be attached to its pendant group at anyheteroatom or carbon atom that results in a stable structure and any ofthe ring atoms can be optionally substituted. Examples of such saturatedor partially unsaturated heterocyclic radicals include, for example,tetrahydrofuranyl, tetrahydrothienyl, pyrrolidinyl, pyrrolidonyl,piperidinyl, pyrrolinyl, tetrahydroquinolinyl, tetrahydroisoquinolinyl,decahydroquinolinyl, oxazolidinyl, piperazinyl, dioxanyl, dioxolanyl,diazepinyl, oxazepinyl, thiazepinyl, morpholinyl, and quinuclidinyl. Theterms “heterocycle”, “heterocyclyl”, “heterocyclyl ring”, “heterocyclicgroup”, “heterocyclic moiety”, and “heterocyclic radical”, are usedinterchangeably herein, and also include groups in which a heterocyclylring is fused to one or more aryl, heteroaryl, or cycloaliphatic rings,such as indolinyl, 3H-indolyl, chromanyl, phenanthridinyl, ortetrahydroquinolinyl, where the radical or point of attachment is on theheterocyclyl ring. A heterocyclyl group may be mono- or bicyclic. Theterm “heterocyclylalkyl” refers to an alkyl group substituted by aheterocyclyl, wherein the alkyl and heterocyclyl portions independentlyare optionally substituted.

As used herein, the term “partially unsaturated” refers to a ring moietythat includes at least one double or triple bond. The term “partiallyunsaturated” is intended to encompass rings having multiple sites ofunsaturation, but is not intended to include aryl or heteroarylmoieties, as herein defined.

As described herein, compounds described herein may contain “optionallysubstituted” moieties. In general, the term “substituted”, whetherpreceded by the term “optionally” or not, means that one or morehydrogens of the designated moiety are replaced with a suitablesubstituent. Unless otherwise indicated, an “optionally substituted”group may have a suitable substituent at each substitutable position ofthe group, and when more than one position in any given structure may besubstituted with more than one substituent selected from a specifiedgroup, the substituent may be either the same or different at everyposition. Combinations of substituents envisioned are preferably thosethat result in the formation of stable or chemically feasible compounds.The term “stable”, as used herein, refers to compounds that are notsubstantially altered when subjected to conditions to allow for theirproduction, detection, and, in some embodiments, their recovery,purification, and use for one or more of the purposes disclosed herein.

In some chemical structures herein, substituents are shown attached to abond which crosses a bond in a ring of the depicted molecule. This meansthat one or more of the substituents may be attached to the ring at anyavailable position (usually in place of a hydrogen atom of the parentstructure). In cases where an atom of a ring so substituted has twosubstitutable positions, two groups may be present on the same ringatom. When more than one substituent is present, each is definedindependently of the others, and each may have a different structure. Incases where the substituent shown crossing a bond of the ring is —R,this has the same meaning as if the ring were said to be “optionallysubstituted” as described in the preceding paragraph.

Suitable monovalent substituents on a substitutable carbon atom of an“optionally substituted” group are independently halogen;—(CH₂)₀₋₄R^(∘); —(CH₂)₀₋₄OR^(∘); —O—(CH₂)₀₋₄C(O)OR^(∘);—(CH₂)₀₋₄CH(OR^(∘))₂; —(CH₂)₀₋₄SR^(∘); —(CH₂)₀₋₄Ph, which may besubstituted with R^(∘); —(CH₂)₀₋₄O(CH₂)₀₋₁Ph which may be substitutedwith R^(∘); —CH—CHPh, which may be substituted with R^(∘); —NO₂; —CN;—N₃; —(CH₂)₀₋₄N(R^(∘))₂; —(CH₂)₀₋₄N(R^(∘))C(O)R^(∘); —N(R^(∘))C(S)R^(∘);—(CH₂)₀₋₄N(R^(∘))C(O)NR^(∘) ₂; —N(R^(∘))C(S)NR^(∘) ₂;—(CH₂)₀₋₄N(R^(∘))C(O)OR^(∘); —N(R^(∘))N(R^(∘))C(O)R^(∘);—N(R^(∘))N(R^(∘))C(O)NR^(∘) ₂; —N(R^(∘))N(R^(∘))C(O)OR^(∘);—(CH₂)₀₋₄C(O)R^(∘); —C(S)R^(∘); —(CH₂)₀₋₄C(O)OR^(∘);—(CH₂)₀₋₄C(O)N(R^(∘))₂; —(CH₂)₀₋₄C(O)SR^(∘); —(CH₂)₀₋₄C(O)OSiR^(∘) ₃;—(CH₂)₀₋₄OC(O)R^(∘); —OC(O)(CH₂)₀₋₄SR^(∘), —SC(S)SR^(∘);—(CH₂)₀₋₄SC(O)R^(∘); —(CH₂)₀₋₄C(O)NR^(∘) ₂; —C(S)NR^(∘) ₂; —C(S)SR^(∘);—SC(S)SR^(∘), —(CH₂)₀₋₄OC(O)NR^(∘) ₂; —C(O)N(OR^(∘))R^(∘);—C(O)C(O)R^(∘); —C(O)CH₂C(O)R^(∘); —C(NOR^(∘))R^(∘); —(CH₂)₀₋₄SSR^(∘);—(CH₂)₀₋₄S(O)₂R^(∘); (CH₂)₀₋₄S(O)₂OR^(∘); —(CH₂)₀₋₄OS(O)₂R^(∘);S(O)₂NR^(∘), —(CH₂)S(O)R^(∘); —N(R^(∘))S(O)₂NR^(∘) ₂;—N(R^(∘))S(O)₂R^(∘); —N(OR^(∘))R^(∘); —C(NH)NR^(∘) ₂; —P(O)₂R^(∘);—P(O)R^(∘); —OP(O)R^(∘) ₂; —OP(O)(OR^(∘))₂; SiR^(∘) ₃; —(C₁₋₄ straightor branched alkylene)O—N(R^(∘))₂; or —(C₁₋₄ straight or branchedalkylene)C(O)O—N(R^(∘))₂, wherein each R^(∘) may be substituted asdefined below and is independently hydrogen, C₁₋₈ aliphatic, —CH₂Ph,—O(CH₂)₀₋₁Ph, or a 5-6-membered saturated, partially unsaturated, oraryl ring having 0-4 heteroatoms independently selected from nitrogen,oxygen, and sulfur, or, notwithstanding the definition above, twoindependent occurrences of R^(∘), taken together with their interveningatom(s), form a 3-12-membered saturated, partially unsaturated, or arylmono- or polycyclic ring having 0-4 heteroatoms independently selectedfrom nitrogen, oxygen, and sulfur, which may be substituted as definedbelow.

Suitable monovalent substituents on R^(∘) (or the ring formed by takingtwo independent occurrences of R^(∘) together with their interveningatoms), are independently halogen, —(CH₂)₀₋₂R^(•), -(haloR^(•)),—(CH₂)₀₋₂OH, —(CH₂)₀₋₂OR^(•), —(CH₂)₀₋₂CH(OR^(•))₂; —O(haloR^(•)), —CN,—N₃, —(CH₂)₀₋₂C(O)R^(•), —(CH₂)₀₋₂C(O)OH, —(CH₂)₀₋₂C(O)OR^(•),—(CH₂)₀₋₄C(O)N(R^(•))₂; —(CH₂)₀₋₂SR^(•), —(CH₂)₀₋₂SH, —(CH₂)₀₋₂NH₂,—(CH)₀₋₂NHR^(•), —(CH₂)₀₋₂NR^(•) ₂, —NO₂, —SiR^(•) ₃, —OSiR^(•) ₃,—C(O)SR^(•), —(C₁₋₄ straight or branched alkylene)C(O)OR^(•), or—SSR^(•) wherein each R^(•) is unsubstituted or where preceded by “halo”is substituted only with one or more halogens, and is independentlyselected from C₁₋₄ aliphatic, —CH₂Ph, —O(CH₂)₀₋₁Ph, or a 5-6-memberedsaturated, partially unsaturated, or aryl ring having 0-4 heteroatomsindependently selected from nitrogen, oxygen, and sulfur. Suitabledivalent substituents on a saturated carbon atom of R^(∘) include ═O and═S.

Suitable divalent substituents on a saturated carbon atom of an“optionally substituted” group include the following: ═O, ═S, ═NNR*₂,═NNHC(O)R*, ═NNHC(O)OR*, ═NNHS(O)₂R*, ═NR*, ═NOR*, —O(C(R*₂))₂₋₃O—, or—S(C(R*₂))₂₋₃S—, wherein each independent occurrence of R is selectedfrom hydrogen, C₁₋₆ aliphatic which may be substituted as defined below,or an unsubstituted 5-6-membered saturated, partially unsaturated, oraryl ring having 0-4 heteroatoms independently selected from nitrogen,oxygen, and sulfur. Suitable divalent substituents that are bound tovicinal substitutable carbons of an “optionally substituted” groupinclude: —O(CR*₂)₂₋₃O—, wherein each independent occurrence of R* isselected from hydrogen, C₁₋₆ aliphatic which may be substituted asdefined below, or an unsubstituted 5-6-membered saturated, partiallyunsaturated, or aryl ring having 0-4 heteroatoms independently selectedfrom nitrogen, oxygen, and sulfur.

Suitable substituents on the aliphatic group of R″ include halogen,—R^(•), -(haloR^(•)), —OH, —OR^(•), —O(haloR^(•)), —CN, —C(O)OH,—C(O)OR^(•), —NH₂, —NHR^(•), —NR^(•) ₂, or —NO₂, wherein each R^(•) isunsubstituted or where preceded by “halo” is substituted only with oneor more halogens, and is independently C₁₋₄ aliphatic, —CH₂Ph,—O(CH₂)₀₋₁Ph, or a 5-6-membered saturated, partially unsaturated, oraryl ring having 0-4 heteroatoms independently selected from nitrogen,oxygen, and sulfur.

Suitable substituents on a substitutable nitrogen of an “optionallysubstituted” group include —R^(†), —NR^(†) ₂, —C(O)R^(†), —C(O)OR^(†),—C(O)C(O)R^(†), —C(O)CH₂C(O)R^(†), —S(O)₂R^(†), —S(O)₂NR^(†) ₂,—C(S)NR^(†) ₂, —C(NH)NR^(†) ₂, or —N(R^(†))S(O)₂R^(†); wherein eachR^(†) is independently hydrogen, C₁₋₆ aliphatic which may be substitutedas defined below, unsubstituted —OPh, or an unsubstituted 5-6-memberedsaturated, partially unsaturated, or aryl ring having 0-4 heteroatomsindependently selected from nitrogen, oxygen, and sulfur, or,notwithstanding the definition above, two independent occurrences ofR^(†), taken together with their intervening atom(s) form anunsubstituted 3-12-membered saturated, partially unsaturated, or arylmono- or bicyclic ring having 0-4 heteroatoms independently selectedfrom nitrogen, oxygen, and sulfur.

Suitable substituents on the aliphatic group of R^(†) are independentlyhalogen, —R^(•), -(haloR^(•)), —OH, —OR^(•), —O(haloR^(•)), —CN,—C(O)OH, —C(O)OR^(•), —NH₂, —NHR^(•), —NR^(•), or —NO₂, wherein eachR^(•) is unsubstituted or where preceded by “halo” is substituted onlywith one or more halogens, and is independently C₁₋₄ aliphatic, —CH₂Ph,—O(CH₂)₀₋₁Ph, or a 5-6-membered saturated, partially unsaturated, oraryl ring having 0-4 heteroatoms independently selected from nitrogen,oxygen, and sulfur.

As used herein, the term “catalyst” refers to a substance the presenceof which increases the rate of a chemical reaction, while not beingconsumed or undergoing a permanent chemical change itself.

As used herein, the term “about” preceding one or more numerical valuesmeans the numerical value ±5%. It should be understood that reference to“about” a value or parameter herein includes (and describes) embodimentsthat are directed to that value or parameter per se. For example,description referring to “about x” includes description of “x” per se.

DETAILED DESCRIPTION

Another route to produce acrylic acid from beta propiolactone (BPL)first polymerizes BPL to poly(propiolactone) (PPL), which is thenisolated and fed into a pyrolysis unit where it thermally decomposes toacrylic acid. The processes and systems described herein provide adirect route for producing acrylic acid from BPL, without isolation ofthe PPL intermediate. Thus, in one aspect, provided is the directconversion of BPL to glacial acrylic acid (e.g., GAA) without isolationof PPL. In some embodiments, provided is concurrent polymerization andpyrolysis steps to directly convert BPL to acrylic acid (e.g., GAA)without isolation of PPL. In certain embodiments, conversion of BPL toPPL is performed in the presence of a polymerization catalyst. In someembodiments, polymerization of BPL to PPL occurs first followed bypyrolysis as part of a continuous process. By avoiding the need toisolate, store, and/or transport PPL, the streamlined preparation ofacrylic acid (e.g., GAA) from BPL offers cost and manufacturingefficiencies that were not previously obtainable.

In certain embodiments, provided are methods for the conversion of BPLto acrylic acid product streams.

I. Methods

In one aspect, provided are integrated processes and methods for theconversion of BPL to acrylic acid. In certain embodiments, provided areintegrated processes for the conversion of BPL to acrylic acid in thepresence of a polymerization catalyst without the need to isolate PPL asa separate intermediate product.

In some embodiments, provided is a method for the synthesis of acrylicacid comprising:

-   -   (a) providing a feedstock stream comprising beta propiolactone;    -   (b) directing the feedstock stream to a reaction zone where the        feedstock stream is contacted with a polymerization catalyst and        where at least a portion of the beta propiolactone is converted        to poly(propiolactone);    -   (c) maintaining the reaction zone at a temperature at or above        the pyrolysis temperature of poly(propiolactone) such that the        thermal decomposition of poly(propiolactone) produces acrylic        acid; and    -   (d) withdrawing an acrylic acid product stream from the reaction        zone;    -   wherein steps (b) and (c) occur in the same reaction zone.

In some embodiments, provided is a method for the synthesis of acrylicacid comprising:

-   -   (a) providing a feedstock stream comprising beta propiolactone;    -   (b) directing the feedstock stream to a first reaction zone        where the feedstock stream is contacted with a polymerization        catalyst and where at least a portion of the beta propiolactone        is converted to a poly(propiolactone) product stream, wherein        the first reaction zone is maintained at a temperature suitable        for the formation of poly(propiolactone);    -   (c) directing the poly(propiolactone) product stream to a second        reaction zone, wherein the second reaction zone is maintained at        a temperature at or above the pyrolysis temperature of        poly(propiolactone) such that the thermal decomposition of        poly(propiolactone) produces acrylic acid; and    -   (d) withdrawing an acrylic acid product stream from the second        reaction zone.

It should generally be understood that reference to “a first reactionzone” or “a second reaction zone”, etc. does not necessarily imply anorder of the reaction zones. In some variations, the use of suchreferences denotes the number of reaction zones present. In othervariations, an order may be implied by the context in which the reactionzones are configured, used or present.

In some variations of the foregoing aspects and embodiments, thepolymerization catalyst is a carboxylate catalyst.

In some embodiments, provided method for producing acrylic acid,comprising:

-   -   (a) providing a feedstock stream comprising beta propiolactone;    -   (b) directing the feedstock stream to a reaction zone;    -   (c) contacting the feedstock stream with a polymerization        catalyst in the reaction zone;    -   (d) converting at least a portion of the beta propiolactone to        poly(propiolactone) in the reaction zone;    -   (e) maintaining the reaction zone at a temperature at or above        the pyrolysis temperature of poly(propiolactone) such that the        thermal decomposition of poly(propiolactone) produces acrylic        acid; and    -   (f) withdrawing an acrylic acid product stream from the reaction        zone;    -   wherein steps (h) and (e) occur in the same reaction zone.

In one embodiment, provided is a method for producing acrylic acid,comprising:

-   -   (a) providing a feedstock stream comprising beta propiolactone;    -   (b) directing the feedstock stream to a reaction zone;    -   (c) contacting the feedstock stream with a polymerization        catalyst in the reaction zone;    -   (d) polymerizing at least a portion of the beta propiolactone to        poly(propiolactone) in the reaction zone, wherein the        temperature of the reaction zone is at or above the pyrolysis        temperature of poly(propiolactone);    -   (e) thermally decomposing the poly(propiolactone) in the        reaction zone to produce acrylic acid; and    -   (f) withdrawing an acrylic acid product stream comprising the        acrylic acid from the reaction zone;    -   wherein steps (b) and (e) occur in the same reaction zone.

In the embodiment described above, the production of thepoly(propiolactone) and the thermal decomposition of thepoly(propiolactone) produced occurs simultaneously in the reaction zone.

The sections below describe more fully certain embodiments of the stepsof the methods and conditions utilized to effect each step.

BPL Conversion to PPL

A beta-lactone feedstock stream used in accordance with provided methodsand systems may be provided from any one or more of a number of knownsources of BPL Methods of making BPL are known in the art and includethose described in WO2013/063191 and WO2014/004858. In some embodiments,a feedstock stream comprising BPL enters a reaction zone describedherein as a gas or as a liquid. The conversion of BPL to PPL may beperformed in either the gas phase or the liquid phase and may beperformed neat, or in the presence of a carrier gas, solvent, or otherdiluent. In some embodiments, a BPL feedstock stream is neat.

It will be appreciated that in certain embodiments, the methods andsystems described herein can also be directly integrated to theformation of ethylene oxide, thus avoiding the isolation and storage ofthis toxic and potentially explosive intermediate. In certainembodiments, the processes described herein are fed by ethylene gaswhich is converted to ethylene oxide, the ethylene oxide then feeds asecond reaction where carbonylation takes place to yield a feedstockstream comprising BPL.

In certain embodiments, conversion of BPL to PPL is performed in acontinuous flow format. In certain embodiments, conversion of BPL to PPLis performed in a continuous flow format in the gas phase. In certainembodiments, conversion of BPL to PPL is performed in a continuous flowformat in the liquid phase. In certain embodiments, conversion of BPL toPPL is performed in a liquid phase in a batch or semi-batch format.Conversion of BPL to PPL may be performed under a variety of conditions.In certain embodiments, the reaction may be performed in the presence ofone or more polymerization catalysts that facilitate the transformationof the BPL to PPL. In one embodiment, the reaction may be performed inthe presence of one or more carboxylate catalysts that facilitate thetransformation of the BPL to PPL.

In certain embodiments, a feedstock stream comprising BPL is directed toa reaction zone where it is contacted with a polymerization catalyst andwhere at least a portion of the BPL is converted to PPL. In oneembodiment, a feedstock stream comprising BPL is directed to a reactionzone where it is contacted with a carboxylate catalyst and where atleast a portion of the BPL is converted to PPL. In some embodiments, thereaction zone is maintained at a temperature suitable for the formationof PPL. In some embodiments, such temperature maintenance comprises theremoval of heat from the reaction zone.

In some embodiments, a feedstock stream comprising BPL is directed to afirst reaction zone where it is contacted with a polymerization catalystand where at least a portion of the BPL is converted to a PPL productstream. In one embodiment, a feedstock stream comprising BPL is directedto a first reaction zone where it is contacted with a carboxylatecatalyst and where at least a portion of the BPL is converted to a PPLproduct stream. In some embodiments, the first reaction zone ismaintained at a temperature suitable for the formation of PPL. In someembodiments, such temperature maintenance comprises the removal of heatfrom the first reaction zone.

In certain embodiments, conversion of BPL to PPL utilizes a solidpolymerization catalyst and the conversion is conducted at leastpartially in the gas phase. In certain embodiments, the solidpolymerization catalyst in the beta lactone conversion stage comprises asolid acrylic acid catalyst. In certain embodiments, BPL is introducedas a liquid and contacted with a solid polymerization catalyst to formPPL, which undergoes pyrolysis and acrylic acid is removed as a gaseousstream. In other embodiments, BPL is introduced as a gas, contacted witha solid polymerization catalyst to form PPL, which undergoes pyrolysisand acrylic acid is removed as a gaseous stream.

In some variations, conversion of BPL to PPL utilizes a solidcarboxylate catalyst and the conversion is conducted at least partiallyin the gas phase. In certain embodiments, the solid carboxylate catalystin the beta lactone conversion stage comprises a solid acrylic acidcatalyst. In certain embodiments, BPL is introduced as a liquid andcontacted with a solid carboxylate catalyst to form PPL which undergoespyrolysis and acrylic acid is removed as a gaseous stream. In otherembodiments, BPL is introduced as a gas, contacted with a solidcarboxylate catalyst to form PPL, which undergoes pyrolysis and acrylicacid is removed as a gaseous stream.

In certain embodiments, processes described herein are characterized inthat the feed rates, reaction rates, and reactor sizes are scaled suchthat each subsequent stage in the process can utilize essentially all ofthe effluent from the previous stage. In certain embodiments, methodsinclude one or more steps of modulating one or more system parametersselected from the group consisting of: the temperature and/or pressureof the lactone conversion stage, the temperature and/or pressure of thepyrolysis stage, and a combination of any two or more of theseparameters. In certain embodiments, this modulation of system parametersis performed such that the conversion rate per unit time of each stagematches that of the previous stage so that the effluent of the previousstage may be used directly to feed the subsequent stage. In certainembodiments, methods include one or more steps of analyzing the effluentfrom one or more stages to assess its content. In certain embodiments,such analyzing steps include performing spectroscopy (e.g., infraredspectroscopy, nuclear magnetic resonance spectroscopy, ultraviolet orvisible light spectroscopy and the like), chromatography (e.g., gas orliquid chromatography). In certain embodiments, such analyzing stepsinclude performing physical analyses (e.g., viscosity measurements,refractive index measurement, density measurement of conductivitymeasurement). In certain embodiments, such analyses are performed in aflow-through or stop-flow mode that provides real-time data on thechemical composition of the effluent. In certain embodiments, such dataare used to provide a prompt to adjust one or more of the systemparameters described above.

As described above, in some embodiments a two-step process is utilizedwhere at least a portion of BPL is converted to a PPL product stream ina first reaction zone, wherein the first reaction zone is maintained ata temperature suitable for the formation of PPL. In some embodiments,the temperature of a first reaction zone is maintained at or below thepyrolysis temperature of polypropiolactone. In some embodiments, thetemperature of a first reaction zone is maintained at or below about150° C. In some embodiments, the temperature of a first reaction zone ismaintained at about 0° C. to about 150° C. In some embodiments, thetemperature of a first reaction zone is maintained at about 25° C. toabout 150° C. In some embodiments, the temperature of a first reactionzone is maintained at about 50° C. to about 150° C. In some embodiments,the temperature of a first reaction zone is maintained at about 75° C.to about 150° C. In some embodiments, the temperature of a firstreaction zone is maintained at about 100° C. to about 150° C. In someembodiments, the temperature of a first reaction zone is maintained atabout 0° C. to about 100° C. In some embodiments, the temperature of afirst reaction zone is maintained at about 50° C. to about 100° C.

PPL Pyrolysis

As described above, in one aspect, BPL is converted to GAA withoutisolation of the intermediate PPL. In some embodiments, the PPL formedby polymerization of BPL is concurrently converted to acrylic acid(e.g., GAA) via pyrolysis in the same reaction zone (e.g., a “one-pot”method). In some embodiments, the reaction zone containing the reactionof BPL to PPL is maintained at a temperature at or above the pyrolysistemperature of PPL such that the thermal decomposition of PPL producesacrylic acid. Without wishing to be bound by any particular theory, itis believed that in such embodiments as BPL reacts with acrylic acid tostart polymer chains, thermal decomposition will degrade the polymer toacrylic acid.

In certain embodiments, a PPL product stream described above as formingin a first reaction zone is directed to a second reaction zone, whereinthe second reaction zone is maintained at a temperature at or above thepyrolysis temperature of PPL such that the thermal decomposition of PPLproduces acrylic acid. In some embodiments, the temperature of a firstreaction zone is different than the temperature of a second reactionzone. In some embodiments, the temperature of a first reaction zone isbelow the pyrolysis temperature of PPL. Such embodiments may also bedescribed as a “two-step” method, wherein at least a portion of BPL isconverted to PPL prior to entering a reaction zone maintained at orabove the pyrolysis temperature. In some embodiments, the PPL productstream entering a second reaction zone comprises an amount of unreactedBPL. In other words, the formation of PPL need not be complete prior toa PPL product stream entering a second reaction zone, and in such casesBPL may undergo polymerization to PPL followed by pyrolysis within thesecond reaction zone.

A one-pot BPL conversion to acrylic acid can be operated within avariety of temperature and pressure ranges. In some embodiments, thetemperature can range from about 150° C. to about 400° C. In someembodiments, the temperature ranges from about 150° C. to about 300° C.In some embodiments, the temperature ranges from about 150° C. to about250° C. In some embodiments, the temperature ranges from about 175° C.to about 300° C. In some embodiments, the temperature ranges from about200° C. to about 250° C. In some embodiments, the temperature rangesfrom about 225° C. to about 275° C. In some embodiments, the temperatureranges from about 250° C. to about 300° C. In some embodiments, thetemperature ranges from about 200° C. to about 300° C.

In some embodiments, a two-step process is utilized where pyrolysisproceeds in a second reaction zone and the second reaction zone ismaintained at a temperature at or above the pyrolysis temperature ofpoly(propiolactone). In some embodiments, the temperature of a secondreaction zone is maintained at or above about 150° C. In someembodiments, the temperature of a second reaction zone is maintained ator above about 160° C. In some embodiments, the temperature of a secondreaction zone is maintained at or above about 175° C. In someembodiments, the temperature of a second reaction zone is maintained ator above about 200° C. In some embodiments, the temperature of a secondreaction zone is maintained at or above about 225° C. In someembodiments, the temperature of a second reaction zone is maintained ator above about 250° C. In some embodiments, the temperature of a secondreaction zone is maintained at or above about 275° C.

In some embodiments, the pressure used in provided methods and systemscan range from about 0.01 atmospheres to about 500 atmospheres(absolute). In some embodiments, the pressure can range from about 0.01atmospheres to about 10 atmospheres (absolute). In some embodiments, thepressure can range from about 0.01 atmospheres to about 50 atmospheres(absolute). In some embodiments, the pressure can range from about 1atmosphere to about 10 atmospheres (absolute). In some embodiments, thepressure can range from about 1 atmosphere to about 50 atmospheres(absolute). In some embodiments, the pressure can range from about 1atmosphere to about 100 atmospheres (absolute). In some embodiments, thepressure can range from about 10 atmospheres to about 50 atmospheres(absolute). In some embodiments, the pressure can range from about 10atmospheres to about 100 atmospheres (absolute). In some embodiments,the pressure can range from about 50 atmospheres to about 100atmospheres (absolute). In some embodiments, the pressure can range fromabout 50 atmospheres to about 200 atmospheres (absolute). In someembodiments, the pressure can range from about 100 atmospheres to about200 atmospheres (absolute). In some embodiments, the pressure can rangefrom about 100 atmospheres to about 250 atmospheres (absolute). In someembodiments, the pressure can range from about 200 atmospheres to about300 atmospheres (absolute). In some embodiments, the pressure can rangefrom about 200 atmospheres to about 500 atmospheres (absolute). In someembodiments, the pressure can range from about 250 atmospheres to about500 atmospheres (absolute).

In some embodiments, the pressure used in provided methods and systemsis less than about 5 atmospheres (absolute). In some embodiments, thepressure used in provided methods and systems is less than about 1atmosphere (absolute). In some embodiments, the pressure can range fromabout 0.01 atmospheres to about 1 atmosphere (absolute). In someembodiments, the pressure can range from about 0.1 atmospheres to about0.8 atmospheres (absolute). In some embodiments, the pressure can rangefrom about 0.1 atmospheres to about 0.5 atmospheres (absolute). In someembodiments, the pressure can range from about 0.01 atmospheres to about0.1 atmospheres (absolute). In some embodiments, the pressure can rangefrom about 0.4 atmospheres to about 1 atmosphere (absolute). In someembodiments, the pressure can range from about 0.05 atmospheres to about0.1 atmospheres (absolute).

In embodiments where there are two reaction zones, they need not beoperated at the same pressure. In certain embodiments the first reactionzone is operated at atmospheric or superatmospheric pressures while thesecond reaction zone is operated at subatmospheric pressure. In certainembodiments a reaction zone can include a pressure gradient.

Reaction Zones

As used herein, the term “reaction zone” refers to a reactor or portionthereof where a particular reaction occurs. A given reaction may occurin multiple reaction zones, and different reaction zones may compriseseparate reactors or portions of the same reactor. A “reactor” typicallycomprises one or more vessels with one or more connections to otherreactors or system components.

In some embodiments of provided methods and systems, a first reactionzone and second reaction zone are comprised within an extruder reactor.In some embodiments, an extruder reactor provides a temperature gradientbetween a first reaction zone and second reaction zone. It will beappreciated that the temperature of a first reaction zone can be lowerthan that of a second reaction zone due to the relative temperaturesneeded to carry out each reaction therein. In some embodiments, anextruder reactor provides a temperature in a first reaction zone ofabout 0° C. to about 150° C., and a temperature in a second reactionzone of about 150° C. to about 300° C. In some embodiments, the terminaltemperature of an extruder is at or above the pyrolysis temperature ofPPL. In some variations, terminal temperature refers to the temperatureat the exit of the extruder.

Polymerization Catalysts

As described above, polymerizing the BPL to PPL proceeds in the presenceof a polymerization catalyst. A variety of catalysts may be used in thepolymerization reaction, including by not limited to metals (e.g.,lithium, sodium, potassium, magnesium, calcium, zinc, aluminum,titanium, cobalt, etc.) metal oxides, salts of alkali and alkaline earthmetals (such as carbonates, borates, hydroxides, alkoxides, andcarboxylates), and borates, silicates, or salts of other metals. Incertain embodiments, suitable catalysts include carboxylate salts ofmetal ions. In certain embodiments suitable catalysts includecarboxylate salts of organic cations. In some embodiments, a carboxylatesalt is other than a carbonate. In some embodiments, a carboxylate saltis acrylate.

In certain embodiments, the polymerization catalyst is combined with BPLin a molar ratio up to about 1:100,000 polymerization catalyst:BPL. Incertain embodiments, the ratio is from about 1:100,000 to about 25:100polymerization catalyst:BPL. In certain embodiments, the polymerizationcatalyst is combined with BPL in a molar ratio of about 1:50,000polymerization catalyst:BPL to about 1:25,000 polymerizationcatalyst:BPL. In certain embodiments, the polymerization catalyst iscombined with BPL in a molar ratio of about 1:25,000 polymerizationcatalyst:BPL to about 1:10,000 polymerization catalyst:BPL. In certainembodiments, the polymerization catalyst is combined with BPL in a molarratio of about 1:20,000 polymerization catalyst:BPL to about 1:10.000polymerization catalyst:BPL. In certain embodiments, the polymerizationcatalyst is combined with BPL in a molar ratio of about 1:15,000polymerization catalyst:BPL to about 1:5,000 polymerizationcatalyst:BPL. In certain embodiments, the polymerization catalyst iscombined with BPL in a molar ratio of about 1:5,000 polymerizationcatalyst:BPL to about 1:1,000 polymerization catalyst:BPL. In certainembodiments, the polymerization catalyst is combined with BPL in a molarratio of about 1:2,000 polymerization catalyst:BPL to about 1:500polymerization catalyst:BPL In certain embodiments, the polymerizationcatalyst is combined with BPI, in a molar ratio of about 1:1,000polymerization catalyst:BPL to about 1:200 polymerization catalyst:BPLIn certain embodiments, the polymerization catalyst is combined with BPLin a molar ratio of about 1:500 polymerization catalyst:BPL to about1:100 polymerization catalyst:BPL In certain embodiments the molar ratioof polymerization catalyst:BPL is about 1:50.000, 1:25,000, 1:15,000,1:10,000, 1:5,000, 1:1,000, 1:500, 1:250 or a range including any two ofthese values. In certain embodiments, the polymerization catalyst iscombined with BPL in a molar ratio of about 1:100 polymerizationcatalyst:BPL to about 25:100 polymerization catalyst:BPL. In certainembodiments the molar ratio of polymerization catalyst:BPL is about1:100, 5:100, 10:100, 15:100, 20:100, 25:100, or a range including anytwo of these ratios.

In certain embodiments, where the polymerization catalyst comprises acarboxylate salt, the carboxylate has a structure such that uponinitiating polymerization of BPL, the polymer chains produced have anacrylate chain end. In certain embodiments, the carboxylate ion on apolymerization catalyst is the anionic form of a chain transfer agentused in the polymerization process.

In certain embodiments, the carboxylate salt of the polymerizationcatalyst is an acrylate salt (i.e., the anionic form) of a compound ofFormula (I):

or a mixture of any two or more of these, where p is from 0 to 9. Incertain embodiments, p is from 0 to 5. In certain embodiments, thecarboxylate salt of the polymerization catalyst is an acrylate salt(i.e., of compound of Formula (I) where p=0).

In certain embodiments, the carboxylate salt of the polymerizationcatalyst is a salt of an acrylic acid dimer,

In certain embodiments, the carboxylate salt of the polymerizationcatalyst is a salt of an acrylic acid trimer,

In certain embodiments, where the polymerization catalyst comprises acarboxylate salt, the carboxylate is the anionic form of a C₁₋₄₀carboxylic acid. In certain embodiments, the carboxylate salt can be asalt of a polycarboxylic acid (e.g. a compound having two or morecarboxylic acid groups). In certain embodiments, the carboxylatecomprises the anion of a C₁₋₂₀ carboxylic acid. In certain embodiments,the carboxylate comprises the anion of a C₁₋₁₂ carboxylic acid. Incertain embodiments, the carboxylate comprises the anion of a C₁₋₈carboxylic acid. In certain embodiments, the carboxylate comprises theanion of a C₁₋₄ carboxylic acid. In certain embodiments, the carboxylatecomprises the anion of an optionally substituted benzoic acid. Incertain embodiments, the carboxylate is selected from the groupconsisting of: formate, acetate, propionate, valerate, butyrate, C₅₋₁₀aliphatic carboxylate, and C₁₀₋₂₀ aliphatic carboxylate.

As noted, in certain embodiments, the polymerization catalyst comprisesa carboxylate salt of an organic cation. In certain embodiments, thepolymerization catalyst comprises a carboxylate salt of a cation whereinthe positive charge is located at least partially on a nitrogen, sulfur,or phosphorus atom. In certain embodiments, the polymerization catalystcomprises a carboxylate salt of a nitrogen cation. In certainembodiments, the polymerization catalyst comprises a carboxylate salt ofa cation selected from the group consisting of: ammonium, amidinium,guanidinium, a cationic form of a nitrogen heterocycle, and anycombination of two or more of these. In certain embodiments, thepolymerization catalyst comprises a carboxylate salt of a phosphoruscation. In certain embodiments, the polymerization catalyst comprises acarboxylate salt of a cation selected from the group consisting of:phosphonium and phosphazenium. In certain embodiments, thepolymerization catalyst comprises a carboxylate salt of asulfur-containing cation. In certain embodiments, the polymerizationcatalyst comprises a sulfonium salt.

In certain embodiments, the polymerization catalyst comprises acarboxylate salt of a metal. In certain embodiments, the polymerizationcatalyst comprises a carboxylate salt of a alkali or alkaline earthmetal. In certain embodiments, the polymerization catalyst comprises acarboxylate salt of an alkali metal. In certain embodiments, thepolymerization catalyst comprises a carboxylate salt of sodium orpotassium. In certain embodiments, the polymerization catalyst comprisesa carboxylate salt of sodium.

In certain embodiments, the polymerization catalyst comprises acarboxylate salt of a protonated amine:

where:

each R¹ and R² is independently hydrogen or an optionally substitutedradical selected from the group consisting of C₁₋₂₀ aliphatic; C₁₋₂₀heteroaliphatic; a 3- to 8-membered saturated or partially unsaturatedmonocyclic carbocycle; a 7- to 14-membered saturated or partiallyunsaturated polycyclic carbocycle; a 5- to 6-membered monocyclicheteroaryl ring having 1-4 heteroatoms independently selected fromnitrogen, oxygen, or sulfur; an 8- to 14-membered polycyclic heteroarylring having 1-5 heteroatoms independently selected from nitrogen,oxygen, or sulfur; a 3- to 8-membered saturated or partially unsaturatedmonocyclic heterocyclic ring having 1-3 heteroatoms independentlyselected from nitrogen, oxygen, or sulfur; a 6- to 14-membered saturatedor partially unsaturated polycyclic heterocycle having 1-5 heteroatomsindependently selected from nitrogen, oxygen, or sulfur; phenyl; or an8- to 14-membered polycyclic aryl ring; wherein R¹ and R² can be takentogether with intervening atoms to form one or more optionallysubstituted rings optionally containing one or more additionalheteroatoms;

each R³ is independently hydrogen or an optionally substituted radicalselected from the group consisting of C₁₋₂₀ aliphatic; C₁₋₂₀heteroaliphatic; a 3- to 8-membered saturated or partially unsaturatedmonocyclic carbocycle; a 7- to 14-membered saturated or partiallyunsaturated polycyclic carbocycle; a 5- to 6-membered monocyclicheteroaryl ring having 1-4 heteroatoms independently selected fromnitrogen, oxygen, or sulfur, an 8- to 14-membered polycyclic heteroarylring having 1-5 heteroatoms independently selected from nitrogen,oxygen, or sulfur; a 3- to 8-membered saturated or partially unsaturatedmonocyclic heterocyclic ring having 1-3 heteroatoms independentlyselected from nitrogen, oxygen, or sulfur; a 6- to 14-membered saturatedor partially unsaturated polycyclic heterocycle having 1-5 heteroatomsindependently selected from nitrogen, oxygen, or sulfur; phenyl; or an8- to 14-membered polycyclic aryl ring; wherein an R³ group can be takenwith an R¹ or R² group to form one or more optionally substituted rings.

In certain embodiments where the polymerization catalyst comprises acarboxylate salt of a protonated amine, the protonated amine is selectedfrom the group consisting of:

In certain embodiments, the polymerization catalyst comprises acarboxylate salt of a quaternary ammonium salt:

where:

-   -   each R¹, R² and R³ is described above; and    -   each R⁴ is independently hydrogen or an optionally substituted        radical selected from the group consisting of C₁₋₂₀ aliphatic;        C₁₋₂₀ heteroaliphatic; a 3- to 8-membered saturated or partially        unsaturated monocyclic carbocycle; a 7- to 14-membered saturated        or partially unsaturated polycyclic carbocycle; a 5- to        6-membered monocyclic heteroaryl ring having 1-4 heteroatoms        independently selected from nitrogen, oxygen, or sulfur; an 8-        to 14-membered polycyclic heteroaryl ring having 1-5 heteroatoms        independently selected from nitrogen, oxygen, or sulfur; a 3- to        8-membered saturated or partially unsaturated monocyclic        heterocyclic ring having 1-3 heteroatoms independently selected        from nitrogen, oxygen, or sulfur; a 6- to 14-membered saturated        or partially unsaturated polycyclic heterocycle having 1-5        heteroatoms independently selected from nitrogen, oxygen, or        sulfur; phenyl; or an 8- to 14-membered polycyclic aryl ring;        wherein an R⁴ group can be taken with an R¹, R² or R³ group to        form one or more optionally substituted rings.

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of a guanidinium group:

wherein each R¹ and R² is independently as defined above and describedin classes and subclasses herein. In certain embodiments, each R¹ and R²is independently hydrogen or C₁₋₂ aliphatic. In certain embodiments,each R¹ and R² is independently hydrogen or C₁₋₁₂ aliphatic. In certainembodiments, each R¹ and R² is independently hydrogen or C₁₋₂₀heteroaliphatic. In certain embodiments, each R¹ and R² is independentlyhydrogen or phenyl. In certain embodiments, each R¹ and R² isindependently hydrogen or 8- to 10-membered aryl. In certainembodiments, each R¹ and R² is independently hydrogen or 5- to10-membered heteroaryl. In certain embodiments, each R¹ and R² isindependently hydrogen or 3- to 7-membered heterocyclic. In certainembodiments, one or more of R¹ and R² is optionally substituted C₁₋₁₂aliphatic.

In certain embodiments, any two or more R¹ or R² groups are takentogether with intervening atoms to form one or more optionallysubstituted carbocyclic, heterocyclic, aryl, or heteroaryl rings. Incertain embodiments, R¹ and R² groups are taken together to form anoptionally substituted 5- or 6-membered ring. In certain embodiments,three or more R¹ and/or R² groups are taken together to form anoptionally substituted fused ring system.

In certain embodiments, an R¹ and R² group are taken together withintervening atoms to form a compound selected from:

wherein each R¹ and R² is independently as defined above and describedin classes and subclasses herein, and Ring G is an optionallysubstituted 5- to 7-membered saturated or partially unsaturatedheterocyclic ring.

It will be appreciated that when a guanidinium cation is depicted as

all such resonance forms are contemplated and encompassed by the presentdisclosure. For example, such groups can also be depicted as

In specific embodiments, a guanidinium cation is selected from the groupconsisting of:

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of a sulfonium group or an arsonium group:

wherein each of R¹, R², and R³ are as defined above and described inclasses and subclasses herein.

In specific embodiments, an arsonium cation is selected from the groupconsisting of:

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of an optionally substituted nitrogen-containingheterocycle. In certain embodiments, the nitrogen-containing heterocycleis an aromatic heterocycle. In certain embodiments, the optionallysubstituted nitrogen-containing heterocycle is selected from the groupconsisting of: pyridine, imidazole, pyrrolidine, pyrazole, quinoline,thiazole, dithiazole, oxazole, triazole, pyrazolem, isoxazole,isothiazole, tetrazole, pyrazine, thiazine, and triazine.

In certain embodiments, a nitrogen-containing heterocycle includes aquaternarized nitrogen atom. In certain embodiments, anitrogen-containing heterocycle includes an iminium moiety such as

In certain embodiments, the optionally substituted nitrogen-containingheterocycle is selected from the group consisting of pyridinium,imidazolium, pyrrolidinium, pyrazolium, quinolinium, thiazolium,dithiazolium, oxazolium, triazolium, isoxazolium, isothiazolium,tetrazolium, pyrazinium, thiazinium, and triazinium.

In certain embodiments, a nitrogen-containing heterocycle is linked to ametal complex via a ring nitrogen atom. In certain embodiments, a ringnitrogen to which the attachment is made is thereby quaternized, and Incertain embodiments, linkage to a metal complex takes the place of anN—H bond and the nitrogen atom thereby remains neutral. In certainembodiments, an optionally substituted N-linked nitrogen-containingheterocycle is a pyridinium derivative. In certain embodiments,optionally substituted N-linked nitrogen-containing heterocycle is animidazolium derivative. In certain embodiments, optionally substitutedN-linked nitrogen-containing heterocycle is a thiazolium derivative. Incertain embodiments, optionally substituted N-linked nitrogen-containingheterocycle is a pyridinium derivative.

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of

In certain embodiments, ring A is an optionally substituted, 5- to10-membered heteroaryl group. In certain embodiments, Ring A is anoptionally substituted, 6-membered heteroaryl group. In certainembodiments, Ring A is a ring of a fused heterocycle. In certainembodiments, Ring A is an optionally substituted pyridyl group.

In specific embodiments, a nitrogen-containing heterocyclic cation isselected from the group consisting of:

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of

where each R¹, R², and R³ is independently as defined above anddescribed in classes and subclasses herein.

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of

wherein each R¹ and R² is independently as defined above and describedin classes and subclasses herein.

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of

wherein each R¹, R², and R³ is independently as defined above anddescribed in classes and subclasses herein.

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of

wherein each of R¹, R², R⁶, and R⁷ is as defined above and described inclasses and subclasses herein.

In certain embodiments, R⁶ and R⁷ are each independently an optionallysubstituted group selected from the group consisting of C₁₋₂₀ aliphatic;C₁₋₂₀ heteroaliphatic; phenyl, and 8-10-membered aryl. In certainembodiments, R⁶ and R⁷ are each independently an optionally substitutedC₁₋₂₀ aliphatic. In certain embodiments, R⁶ and R⁷ are eachindependently an optionally substituted C₁₋₂₀ heteroaliphatic having. Incertain embodiments, R⁶ and R⁷ are each independently an optionallysubstituted phenyl or 8-10-membered aryl. In certain embodiments, R⁶ andR⁷ are each independently an optionally substituted 5- to 10-memberedheteroaryl. In certain embodiments, R⁶ and R⁷ can be taken together withintervening atoms to form one or more rings selected from the groupconsisting of: optionally substituted C₃-C₁₄ carbocycle, optionallysubstituted C₃-C₁₄ heterocycle, optionally substituted C₆-C₁₀ aryl, andoptionally substituted 5- to 10-membered heteroaryl. In certainembodiments, R⁶ and R⁷ are each independently an optionally substitutedC₁₋₆ aliphatic. In certain embodiments, each occurrence of R⁶ and R⁷ isindependently methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl,octyl, or benzyl. In certain embodiments, each occurrence of R⁶ and R⁷is independently perfluoro. In certain embodiments, each occurrence ofR⁶ and R⁷ is independently —CF₂CF₃.

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of

wherein each R¹ and R² is independently as defined above and describedin classes and subclasses herein.

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of

wherein each R¹, R², and R³ is independently as defined above anddescribed in classes and subclasses herein.

In certain embodiments, a cation is

wherein each R¹ and R² is independently as defined above and describedin classes and subclasses herein.

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of

wherein each R¹ and R² is independently as defined above and describedin classes and subclasses herein.

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of

wherein each R¹, R², and R³ is independently as defined above anddescribed in classes and subclasses herein.

In certain embodiments, a polymerization catalyst comprises acarboxylate salt of

wherein each R¹ and R² is independently as defined above and describedin classes and subclasses herein. In certain embodiments, suitablecatalysts include transition metal compounds. In certain embodiments,suitable catalysts include acid catalysts. In certain embodiments, thecatalyst is a heterogeneous catalyst.

In certain embodiments, any of the foregoing cationic functional groupsare attached to a solid support. Examples of suitable solid supportsinclude polymeric solids (e.g. polymer beads, films, fibers, fabric,particles and the like) as well as inorganic solids (e.g. clays,silicas, aluminas, diatomaceous earth, ceramics, metal oxides, mineralfibers beads or particles, and the like). Specific examples of suchsupported cationic functional groups include polystyrene resin beadsfunctionalized with ammonium groups, polystyrene resin beadsfunctionalized with phosphonium groups, and polystyrene resin beadsfunctionalized with guanidinium groups. Specific examples of suchsupported cationic functional groups include silica particlesfunctionalized with ammonium groups, alumina particles functionalizedwith phosphonium groups, and ceramic beads functionalized withguanidinium groups. In certain embodiments, polymerization catalystscomprise carboxylate salts of any of the foregoing supported solidcationic functional groups. In certain embodiments, polymerizationcatalysts comprise acrylate salts of any of the foregoing supportedsolid cationic functional groups.

In certain embodiments, polymerization catalysts comprise cationicsolids wherein the cations comprise metal atoms. In certain embodiments,polymerization catalysts comprise carboxylate salts of any of theforegoing supported solid cationic metal atoms. In certain embodiments,polymerization catalysts comprise acrylate salts of any of the foregoingsupported solid cationic metal atoms.

In certain embodiments, the carboxylate salt of the polymerizationcatalyst is a compound of Formula (II):

where p is from 0 to 9 and R^(a) is a non-volatile moiety. The term“non-volatile moiety,” as used herein, refers to a moiety or material towhich a carboxylate can be attached, and that renders the carboxylate(e.g., when p=0) non-volatile to pyrolysis conditions. In someembodiments, a non-volatile moiety is selected from the group consistingof glass surfaces, silica surfaces, plastic surfaces, metal surfacesincluding zeolites, surfaces containing a metallic or chemical coating,membranes (e.g., nylon, polysulfone, silica), micro-beads (e.g., latex,polystyrene, or other polymer), and porous polymer matrices (e.g.,polyacrylamide, polysaccharide, polymethacrylate). In some embodiments,a non-volatile moiety has a molecular weight above 100, 200, 500, or1000 g/mol. In some embodiments, a non-volatile moiety is part of afixed or packed bed system. In some embodiments, a non-volatile moietyis part of a fixed or packed bed system comprising pellets (e.g.,zeolite).

In certain embodiments, p is from 0 to 5. In certain embodiments, thecarboxylate salt of the polymerization catalyst is an acrylate salt(i.e., of compound of Formula (II) where p=0).

In some embodiments, a suitable polymerization catalyst isheterogeneous. In some embodiments, a suitable polymerization catalystwill remain in a reaction zone as a salt or melt after removal of allother products, intermediates, starting materials, byproducts, and otherreaction components. In some embodiments, a suitable polymerizationcatalyst of Formula (II) will remain in a reaction zone as a salt ormelt after removal of all acrylic acid product stream.

In certain embodiments, a catalyst is recycled for further use in areaction zone. In some embodiments, a salt or melt catalyst is recycledto a reaction zone. In some embodiments, provided methods furthercomprise withdrawing a recycling stream of homogeneous catalyst from areaction zone. In some embodiments, such a recycling stream comprises ahigh boiling solvent, wherein the solvent's boiling point is above thepyrolysis temperature of PPL and the catalyst remains in the highboiling solvent during pyrolysis while the withdrawn product stream isgaseous.

Acrylate Recycling

It will be appreciated by the skilled artisan that the polymerizationmode of PPL from BPL proceeds in a manner contrary to the typicalpolyester polymerization. While polyesters are generally formed by theattack of a hydroxyl group at the carbonyl of a carboxylic group, thestrain of the BPL ring affords a unique reactivity wherein a carboxylateanion attacks at the beta carbon, resulting in a terminal carboxylatewhich may then react with another unit of BPL to propagate the polymerchain:

In some embodiments of provided methods, the polymerization of BPL toPPL is catalyzed by an acrylate. Resulting polymer chains will thencomprise acrylate end groups. In some embodiments, a carboxylaterequired to initiate polymerization is acrylic acid provided via areturn loop from a product stream. In some embodiments, a portion ofacrylic acid produced by a provided method is returned to a reactionzone to initiate polymerization. In some embodiments, acrylic acidformed in situ in a provided method is sufficient to initiate andmaintain the conversion of BPL to PPL.

Heat Capturing

In some embodiments of provided methods, heat generated from one portionof a process is captured. For example, polymerization of BPL to PPL isan exothermic process and excess heat generated from the reaction may becaptured. In certain embodiments, captured heat is low grade heat. Insome embodiments of provided methods, heat generated from a firstreaction zone is captured and directed to other processes. In certainembodiments, heat is directed to a second reaction zone. In certainembodiments, heat is directed to an upstream carbonylation process usedto provide BPL. In some embodiments, heat is directed to keep a productstream (e.g., acrylic acid vapor) at an appropriate temperature.

Reaction Mode

The methods herein place no particular limits on the type, size orgeometry of the reactor employed and indeed, in some cases, more thanone reactor may be employed. It is to be understood that the term“reactor” as recited in the methods herein may actually represent morethan one physical reactor (for example the reactor could be a train ofcontinuous stirred tank reactors (CSTRs) connected in parallel or inseries, or a plurality of plug flow reactors). In some embodiments, the“reactor” referred to in the methods herein may also comprise more thanone type of reactor (for example the reactor could comprise a series ofextruder reactors). Many such combinations are known in the art andcould be employed by the skilled artisan to achieve an efficientreaction in the methods described herein.

Solvents

As used herein, the term “high boiling solvent” refers to a solventhaving a boiling point higher than that of the pyrolysis temperature ofPPL. In some embodiments, a high boiling point solvent has a boilingpoint higher than 150° C. In some embodiments, a high boiling pointsolvent has a boiling point higher than 180° C. In some embodiments, ahigh boiling point solvent has a boiling point higher than 200° C. Insome embodiments, a high boiling point solvent has a boiling pointhigher than 220° C. Boiling points used herein are the boiling points ata pressure of 1 atm.

II. Systems

In another aspect, provided are systems for the synthesis of acrylicacid. In some embodiments, a system for the conversion of betapropiolactone to acrylic acid comprises:

-   -   (a) beta propiolactone (BPL); and    -   (b) a cationic solid catalyst comprising a carboxylate salt,    -   wherein at or above the pyrolysis temperature of        poly(propiolactone) (PPL), BPL begins polymerizing to PPL in the        presence of the cationic solid catalyst, which PPL concurrently        thermally decomposes to acrylic acid;    -   wherein acrylic acid formed in situ maintains the reaction        polymerizing BPL to PPL.

In some variations, provided is a system for converting betapropiolactone to acrylic acid, comprising:

-   -   a beta propiolactone (BPL) source;    -   a catalyst source; and    -   a reactor comprising:        -   at least one inlet to receive BPL from the BPL source and a            polymerization catalyst from the catalyst source, wherein            the polymerization catalyst comprises a carboxylate salt,            and        -   an outlet to output an acrylic acid stream,    -   wherein the reactor is configured to (i) polymerize the BPL to        produce poly(propiolactone) (PPL) in the presence of the        polymerization catalyst, at or above the pyrolysis temperature        of PPL, and (ii) concurrently thermally decompose the PPL to        produce acrylic acid in situ, and wherein the acrylic acid        produced in situ maintains the polymerization of BPL to PPL.

In some embodiments, the polymerization catalyst is a cationic solidcatalyst comprising a carboxylate salt.

As mentioned above, in some embodiments provided methods comprise areturn loop of acrylic acid product to a reactor. Thus, in someembodiments, a system for the conversion of beta propiolactone toacrylic acid comprises:

-   -   (a) a reaction zone comprising beta propiolactone (BPL) and a        polymerization catalyst comprising a carboxylate salt;    -   wherein at or above the pyrolysis temperature of        poly(propiolactone) (PPL), BPL begins polymerizing to PPL, which        PPL concurrently thermally decomposes to acrylic acid; and    -   (b) a return loop for providing acrylic acid to the reaction        zone.

In some variations, provided is a system for converting betapropiolactone to acrylic acid, comprising:

-   -   a reaction zone comprising beta propiolactone (BPL) and a        cationic solid catalyst comprising a carboxylate salt, wherein        the reaction zone is configured to (i) polymerize BPL to        poly(propiolactone) (PPL) in the presence of the cationic solid        catalyst, at or above the pyrolysis temperature of PPL, and (ii)        concurrently thermally decomposes the PPL to acrylic acid; and    -   a return loop for providing acrylic acid to the reaction zone.

It should be understood that any of the cationic solid catalystsdescribed herein may be used in the systems of the foregoing embodimentsand variations.

ENUMERATED EMBODIMENTS

The following enumerated embodiments are representative of some aspectsof the invention.

1. A method for the synthesis of acrylic acid comprising the steps of:

-   -   (a) providing a feedstock stream comprising beta propiolactone;    -   (b) directing the feedstock stream to a reaction zone where it        is contacted with a suitable carboxylate catalyst and where at        least a portion of the beta propiolactone is converted to        poly(propiolactone);    -   (c) maintaining the reaction zone at a temperature at or above        the pyrolysis temperature of poly(propiolactone) such that the        thermal decomposition of poly(propiolactone) produces acrylic        acid; and    -   (d) withdrawing an acrylic acid product stream from the reaction        zone;    -   wherein steps (b) and (c) occur in the same reaction zone.        2. The method of embodiment 1, further comprising directing a        return loop of a portion of the acrylic acid product stream to        the reaction zone.        3. A method for the synthesis of acrylic acid comprising the        steps of:    -   (a) providing a feedstock stream comprising beta propiolactone;    -   (b) directing the feedstock stream to a first reaction zone        where it is contacted with a suitable carboxylate catalyst and        where at least a portion of the beta propiolactone is converted        to a poly(propiolactone) product stream, wherein the first        reaction zone is maintained at a temperature suitable for the        formation of poly(propiolactone);    -   (c) directing the poly(propiolactone) product stream to a second        reaction zone, wherein the second reaction zone is maintained at        a temperature at or above the pyrolysis temperature of        poly(propiolactone) such that the thermal decomposition of        poly(propiolactone) produces acrylic acid; and    -   (d) withdrawing an acrylic acid product stream from the second        reaction zone.        4. The method of embodiment 2, wherein the first reaction zone        and second reaction zone are comprised within an extruder        reactor.        5. The method of embodiment 4, wherein the extruder reactor        provides a temperature gradient between the first reaction zone        and second reaction zone.        6. The method of embodiment 5, wherein the terminal temperature        of the extruder is at or above the pyrolysis temperature of        poly(propiolactone).        7. The method of any one of embodiments 3-6, further comprising        the step of capturing heat generated from the first reaction        zone and directing the heat to other processes.        8. The method of embodiment 7, wherein the heat is directed to        the second reaction zone.        9. The method of any one of the preceding embodiments, wherein        the suitable carboxylate catalyst is a salt of a compound of        formula:

wherein p is 0 to 9.10. The method of any one of embodiments 1-8, wherein the suitablecarboxylate catalyst is a salt of a compound of formula:

where p is from 0 to 9 and R^(a) is a non-volatile moiety.11. The method of any one of the preceding embodiments, wherein thesuitable carboxylate catalyst is heterogeneous.12. The method of any one of the preceding embodiments, wherein afterremoval of all acrylic acid product stream, the suitable carboxylatecatalyst remains in the reaction zone as a salt or melt.13. The method of embodiment 12, wherein the salt or melt is thenrecycled to the reaction zone.14. The method of any one of the preceding embodiments, wherein thefeedstock stream contains or is combined with a high boiling solvent.15. The method of embodiment 14, further comprising the step ofwithdrawing a recycling stream of the suitable carboxylate catalyst tothe reaction zone.16. The method of any one of the preceding embodiments, furthercomprising directing a return loop of a portion of the acrylic acidproduct stream to the reaction zone.17. The method of any one of the preceding embodiments, wherein the betapropiolactone feedstock stream is neat.18. A system for the conversion of beta propiolactone to acrylic acidcomprising:

-   -   (a) beta propiolactone; and    -   (b) a cationic solid catalyst comprising a carboxylate salt;    -   wherein at or above the pyrolysis temperature of        poly(propiolactone), beta propiolactone begins polymerizing to        poly(propiolactone) in the presence of the cationic solid        catalyst, which poly(propiolactone) concurrently thermally        decomposes to acrylic acid; and    -   wherein acrylic acid formed in situ maintains the reaction        polymerizing beta propiolactone to poly(propiolactone).        19. A system for the conversion of beta propiolactone to acrylic        acid comprising:    -   (a) a reaction zone comprising beta propiolactone (BPL) and a        cationic solid catalyst comprising a carboxylate salt;    -   wherein at or above the pyrolysis temperature of        poly(propiolactone) (PPL), BPL begins polymerizing to PPL, which        PPL concurrently thermally decomposes to acrylic acid; and    -   (b) a return loop for providing acrylic acid to the reaction        zone.        20. A method for producing acrylic acid, comprising:    -   (a) providing a feedstock stream comprising beta propiolactone;    -   (b) directing the feedstock stream to a reaction zone;    -   (c) contacting the feedstock stream with a polymerization        catalyst in the reaction zone;    -   (d) polymerizing at least a portion of the beta propiolactone to        poly(propiolactone) in the reaction zone, wherein the        temperature of the reaction zone is at or above the pyrolysis        temperature of poly(propiolactone);    -   (e) thermally decomposing the poly(propiolactone) in the        reaction zone to produce acrylic acid; and    -   (f) withdrawing an acrylic acid product stream comprising the        acrylic acid from the reaction zone;    -   wherein steps (b) and (e) occur in the same reaction zone.        21. The method of embodiment 20, further comprising directing a        return loop comprising a portion of the acrylic acid product        stream to the reaction zone.        22. The method of embodiment 21, wherein the return loop of        acrylic acid is combined with the feedstock stream.        23. A method for producing acrylic acid, comprising:    -   (a) providing a feedstock stream comprising beta propiolactone;    -   (b) directing the feedstock stream to a first reaction zone;    -   (c) contacting the feedstock stream with a polymerization        catalyst;    -   (d) polymerizing at least a portion of the beta propiolactone to        a poly(propiolactone) product stream, wherein the first reaction        zone is maintained at a temperature to promote formation of        poly(propiolactone);    -   (e) directing the poly(propiolactone) product stream to a second        reaction zone, wherein the second reaction zone is maintained at        a temperature at or above the pyrolysis temperature of        poly(propiolactone) such that the thermal decomposition of        poly(propiolactone) produces acrylic acid; and    -   (f) withdrawing an acrylic acid product stream from the second        reaction zone.        24. The method of embodiment 23, wherein the first reaction zone        and second reaction zone are in an extruder reactor.        25. The method of embodiment 24, wherein the extruder reactor        provides a temperature gradient between the first reaction zone        and second reaction zone.        26. The method of embodiment 24 or 25, wherein the extruder        reactor has a terminal temperature at or above the pyrolysis        temperature of poly(propiolactone).        27. The method of any one of embodiments 23 to 26, further        comprising capturing heat generated from the first reaction        zone, and directing the heat to other processes.        28. The method of embodiment 27, wherein the heat is directed to        the second reaction zone.        29. The method of any one of embodiments 20 to 28, wherein the        polymerization catalyst is a salt of a compound of formula:

wherein p is 0 to 9.30. The method of any one of embodiments 20 to 28, wherein thepolymerization catalyst is a salt of a compound of formula:

where p is from 0 to 9 and R^(a) is a non-volatile moiety.31. The method of any one of embodiments 20 to 30, wherein thepolymerization catalyst is heterogeneous.32. The method of any one of embodiments 20 to 31, wherein after removalof all acrylic acid product stream, the polymerization catalyst remainsas a salt or melt.33. The method of embodiment 32, further comprising recycling the saltor melt to the reaction zone.34. The method of any one of embodiments 20 to 33, wherein the feedstockstream contains or is combined with a high boiling solvent.35. The method of embodiment 34, further comprising withdrawing arecycling stream of the polymerization catalyst from the reaction zone.36. The method of any one of embodiments 20 to 35, further comprisingdirecting a return loop of a portion of the acrylic acid product streamto the reaction zone.37. The method of any one of embodiments 20 to 36, wherein the feedstockstream is neat.38. A system for converting beta propiolactone to acrylic acid,comprising:

-   -   (a) beta propiolactone; and    -   (b) a cationic solid catalyst comprising a carboxylate salt,    -   wherein at or above the pyrolysis temperature of        poly(propiolactone), beta propiolactone begins polymerizing to        poly(propiolactone) in the presence of the cationic solid        catalyst, which poly(propiolactone) concurrently thermally        decomposes to acrylic acid, and    -   wherein acrylic acid formed in situ maintains the reaction        polymerizing beta propiolactone to poly(propiolactone).        39. A system for converting beta propiolactone to acrylic acid,        comprising:    -   (a) a reaction zone comprising beta propiolactone (BPL) and a        cationic solid catalyst comprising a carboxylate salt,    -   wherein at or above the pyrolysis temperature of        poly(propiolactone) (PPL), BPL begins polymerizing to PPL, which        PPL concurrently thermally decomposes to acrylic acid; and    -   (b) a return loop for providing acrylic acid to the reaction        zone.        40. The system of embodiment 38 or 39, wherein the carboxylate        salt is:    -   a salt of a compound of formula:

wherein p is 0 to 9; or

-   -   a salt of a compound of formula:

where p is from 0 to 9 and R^(a) is a non-volatile moiety.

1-3. (canceled)
 4. A method for producing acrylic acid, comprising: (a)providing a feedstock stream comprising beta propiolactone; (b)directing the feedstock stream to a first reaction zone; (c) contactingthe feedstock stream with a polymerization catalyst; (d) polymerizing atleast a portion of the beta propiolactone to a poly(propiolactone)product stream, wherein the first reaction zone is maintained at atemperature to promote formation of poly(propiolactone); (e) directingthe poly(propiolactone) product stream to a second reaction zone,wherein the second reaction zone is maintained at a temperature at orabove the pyrolysis temperature of poly(propiolactone) such that thethermal decomposition of poly(propiolactone) produces acrylic acid; and(f) withdrawing an acrylic acid product stream from the second reactionzone.
 5. The method of claim 4, wherein the first reaction zone andsecond reaction zone are in an extruder reactor.
 6. The method of claim5, wherein the extruder reactor provides a temperature gradient betweenthe first reaction zone and second reaction zone.
 7. The method of claim5, wherein the extruder reactor has a terminal temperature at or abovethe pyrolysis temperature of poly(propiolactone).
 8. The method of claim4, further comprising capturing heat generated from the first reactionzone, and directing the heat to other processes.
 9. The method of claim8, wherein the heat is directed to the second reaction zone. 10-18.(canceled)
 19. A system for converting beta propiolactone to acrylicacid, comprising: (a) a beta propiolactone source; (b) a catalystsource; and (c) a reactor comprising: at least one inlet to receive betapropiolactone from the beta propiolactone source and a polymerizationcatalyst from the catalyst source, wherein the polymerization catalystcomprises a carboxylate salt, and an outlet to output an acrylic acidstream, wherein the reactor is configured to (i) polymerize the betapropiolactone to produce poly(propiolactone) in the presence of thepolymerization catalyst, at or above the pyrolysis temperature ofpoly(propiolactone), and (ii) concurrently thermally decompose thepoly(propiolactone) to produce acrylic acid in situ, and wherein theacrylic acid produced in situ maintains the polymerization of betapropiolactone to poly(propiolactone).
 20. A system for converting betapropiolactone to acrylic acid, comprising: (a) a reaction zonecomprising beta propiolactone and a cationic solid catalyst comprising acarboxylate salt, wherein the reaction zone is configured to (i)polymerize the beta propiolactone to poly(propiolactone), at or abovethe pyrolysis temperature of poly(propiolactone), (ii) concurrentlythermally decompose the poly(propiolactone) to acrylic acid, and (iii)output the acrylic acid; and (b) a return loop configured to return aportion of the acrylic acid to the reaction zone to maintainpolymerization of the beta propiolactone to poly(propiolactone) in thereaction zone.
 21. The system of claim 19, wherein the carboxylate saltis: a salt of a compound of formula:

wherein p is 0 to
 9. 22. The system of claim 19, wherein the carboxylatesalt is: a salt of a compound of formula:

where p is from 0 to 9 and R^(a) is a non-volatile moiety.
 23. Thesystem of claim 20, wherein the carboxylate salt is: a salt of acompound of formula:

wherein p is 0 to
 9. 24. The system of claim 20, wherein the carboxylatesalt is: a salt of a compound of formula:

where p is from 0 to 9 and R^(a) is a non-volatile moiety.